I have found that the warmer you keep the tank the less likely ick will set in when adding fish, I keep mine between 80 - 82 degrees, but that is because I have clown loaches and they like it a little warmer.
The lower the temp (low to mid 70's) the more likely to bring on ick..
I have also notice that lower temps bring on more sluggish fish, higher temps bring on more active fish...
This is just my observation....